Method of Installing Sealed Circular Ductwork

ABSTRACT

A circular sheet metal duct having a sealant applied across the longitudinal seam. The sealant will improve the efficiency and will reduce or eliminate air leakage from the longitudinal seam. The sealant is applied during the manufacturing processes so that an installer does not have to seal the duct work. The method of manufacturing the sealant is provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of prior application Ser. No.13/335,188, filed Dec. 22, 2011, which in turn is a Divisional ofapplication Ser. No. 12/041,865, filed Mar. 4, 2008, which issued asU.S. Pat. No. 8,151,430 on Apr. 10, 2012, which in turn is a Divisionalof application Ser. No. 11/739,238, filed Apr. 24, 2007, which issued asU.S. Pat. No. 7,478,467 on Jan. 20, 2009 and which claims the benefit ofU.S. Provisional Application No. 60/746,573, filed May 5, 2006.application Ser. No. 13/335,188, application Ser. No. 12/041,865, nowU.S. Pat. No. 8,151,430, application Ser. No. 11/739,238, now U.S. Pat.No. 7,478,467, and U.S. Provisional Application No. 60/746,573 arehereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to ducts used in the heating, ventilating,exhaust and/or air conditioning fields.

Description of Related Art

Ducts having circular, rectangular, or other cross sectional shape areused to transport heated or cooled air or other gasses from one place toanother. A typical example is heated or cooled air from an airconditioner or furnace is transported to individual locations by a duct.These types of ducts are formed from sheet metal. The sheet metal isformed into a particular shape by taking ends of the sheet metal andinterlocking them.

In circular duct work it is most common to have a self locking type ofseam on the duct work that is put together by an installer. Typicalexamples of self locking mechanisms are reeves locks and button locks.

Previously, liquid (mastic) sealant was used for sealing rectangularduct work. Rectangular duct work is typically sold made to order.Manufacturers of rectangular ducts will manufacture the duct work to thespecification of the installer. Therefore when supplying sealedrectangular ductwork it is already constructed prior to being shippedand the sealant is never exposed.

Circular duct work with reeves locks or button locks is typicallyshipped in bundles. An installer will then remove individual pieces fromthe bundle and then snap the seam of the duct together via theinterlocking mechanism to create a circular duct. 5′ pieces are shippedwith 1 piece locked with 4 pieces around it for a total of 5. 2′ piecesare shipped with 1 piece locked with 9 pieces around it for a total of10 pieces. On some small sizes, all of the pieces can be locked.

However, these types of self locking mechanisms leak and causeinefficiency. This is problematic because of the cost of energy. Aliquid sealant would not work with circular duct work having a selflocking mechanism because the machines that manufacture the circularductwork are not compatible with liquid sealant. The machines thatmanufacture circular ducts cannot use a liquid sealant because theliquid sealant will tend to flow or string outside of the applied areaand onto the forming rolls. Once on the forming rolls, the machinerywill not function properly. Because circular duct is shipped in bundles,parts of the duct where the liquid sealant is applied contact otherparts of the duct. This causes the liquid sealant to adhere to theinterior and/or exterior of the duct. The excess liquid sealant servesas dirt collection points for ducts in service and extra cleaningrequirements for the exterior of exposed duct systems. No installerwould buy circular duct work with a liquid sealant because the messcreated by the liquid sealant would require additional cleaning.Additionally, when circular duct work is installed it may have to be cutby the installer. The cutting is done with the self locking mechanismdisengaged. It sometimes becomes necessary for the installer to engagethe self locking mechanism and then to disengage it. This is notpossible with the liquid sealant that has been used in square duct work.If the liquid sealant is used with circular duct having a self lockingmechanism and the self locking mechanism is disengaged, the integrity ofthe sealant would be compromised, thus causing failure to seal whenre-engaged. Additionally, the sealant will be all over the inside andoutside of the duct which will contaminate the air flow and can alsocollect dust on both the inside and outside of the duct. The collectionof dust inside the duct can lead to mold growth, potentially creatingindoor air quality hazards. The excess liquid sealant on the outside ofthe duct creates difficulty in painting the duct or resealing the ductas it could react with paint or sealant. The liquid sealant also offgasses VOCs into the air. Therefore, the liquid sealant is not used withcircular duct work and there is no known circular duct work that is soldwith sealant already applied.

Currently if a self locking circular sealed system is required, theinstaller assembles the ductwork and then has to use additionalmaterials, such as tape or sealant and labor to have a sealed system.

There is a need for a sealed self locking circular system that does notrequire the installer to seal or tape the ductwork in order to reduceenergy consumption and create efficiency.

BRIEF SUMMARY OF THE INVENTION

This invention provides a sheet metal duct having a sealant and providesa method of manufacturing the sheet metal duct with the sealant. Thesheet metal duct is formed by an interlocking mechanism which is made upof a female portion and a male portion on ends of the sheet metal thatengage each other. Sealant is placed in either the female portion or themale portion of the interlocking mechanism. The sealant could be a foamsealant and the sealant could be a type of sealant that allows aninstaller to disengage and then reengage the interlocking mechanism. Thesealant could also be the type that requires tape or that does notrequire tape. The locking mechanism could be a reeves lock or a buttonlock pursuant to SMACNA Rules 6a, 6b, 7 and 8.

This invention also provides for a method for manufacturing a sheetmetal duct. Sheet metal having a snap lock mechanism is provided.Sealant is inserted into the snap lock mechanism. The sheet metal isthen formed into a duct. The sheet metal could be provided in strips.The snap lock mechanism could be formed into the sheet metal by aforming machine. The snap locking mechanism can have a male portion anda female portion that is created by the forming machine rolls. Thesealant could be inserted into the female portion. The female portioncan be created by folding the sheet metal to create a fold having a gap.The forming could be done by multiple rolls, each roll forming the sheetmetal further lessening the angle of the gap until the desired angle gapis created. The sealant can be inserted into the gap when the angle ofthe gap is between ninety (90) and ten (10) degrees. The sealant can beinserted by a nozzle in between the second (2^(nd)) and eighth (8^(th))roll.

An object of this invention is to provide a sealed duct system directlyfrom the manufacturer without requiring the installer to take additionalsteps such as applying sealant or tape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross section side view of a disengaged button lock withsealant.

FIG. 2 shows a cross section side view of an engaged button lock withsealant.

FIG. 3 shows a flow chart of the manufacturing process.

FIG. 4 shows roll stand 1 with sheet metal.

FIG. 5 shows roll stand 2 with sheet metal.

FIG. 6 shows roll stand 3 with sheet metal

FIG. 7 shows rolls stand 4 with sheet metal.

FIG. 8 shows roll stand 5 with sheet metal.

FIG. 9 shows roll stand 6 with sheet metal and the nozzle inserting thesealant in between roll stand 5 and roll stand 6.

FIG. 10 shows roll stand 7 with the sheet metal having a sealant.

FIG. 11 shows roll stand 8 with the sheet metal having a sealant.

FIG. 12 is a chart of showing leakage rates of sealed vs. unsealed.

FIG. 13 is chart showing the percent leakage.

FIG. 14 is the nozzle.

FIG. 15 shows tables a, b, and c showing the experimental pressure andleakage data.

DETAILED DESCRIPTION Examples and Explanatory Definitions

“sheet metal duct”—Metal in the form of a sheet that is formed into apipe, tube, or channel that conveys a substance.

“circular sheet metal duct”—A pipe, tube, or channel that conveys air ora gas having a circular cross section. This can be round or oval.

“self sealing”—Sealing without the installer having to take anyadditional steps outside of normal installation of circular duct.

“HVAC sealant”—Something that limits air leakage through a joint.

“a liquid applied gasketing sealant”—Any sealant that is applied as aliquid and then solidifies to have sufficient compressibility so that itcan form an air tight seal. After the sealant solidifies it hardens tothe point where it can compress to make a seal. It is sufficiently hardso that when the self locking mechanism is engaged the sealant will notflow or displace itself out of the applied area, as would happen if aliquid sealant were used. The sealant is formulated with blockco-polymers. Examples are butyl and E.P.D. M. rubbers. The sealant couldalso be a polyurethane foamed in place sealant. Any sealant used isapplied as a liquid and forms a gasket. This type of sealant does notstring like the mastic sealants do. Because the sealants do not string,this process prevents waste during the application process.

“the sealant has physical properties such that it provides a reusableseal”-A person must be able to close the snap locking mechanism thatforms a sealed duct and then undo the locking mechanism and then againclose the locking mechanism to create a sealed duct. It can be anysealant that has sufficient cohesive strength to be able to be usedrepeatedly and have sufficient compressibility so that it can form anair tight seal. The sealant must allow the lock to be able to be openedand closed repeatedly. The sealant is applied as a liquid and thensolidifies. After the sealant solidifies it hardens to the point whereit compresses to make a seal. There is no flow around or displacementsuch as when a liquid applied sealant is used.

“engaged”—The male and female portions of the locking mechanism areconnected.

“disengaged”—The male and female portions of the locking mechanism areseparated from the engaged position.

“reengaged”—The male and female portions of the locking mechanisms areconnected after having been previously connected and disconnected.

“sealed duct”—A duct that is designed or modified through the additionof sealants to prevent or eliminate leakage of air through the seam(s)in the boundary wall of the duct.

“self locking mechanism”—Something that allows two edges of sheet metalto be joined together without a separate fastener to form a duct. Theseam created by the edges is referred to as the longitudinal seam.Examples of this are a button lock and a reeves lock. (see SMACNA Rules6a, 6b, 7 and 8)

“a female portion”—Is the part of the connection that receives the otherend.

“a male portion”—Is the part of the connection that inserts into theend.

“on edges of the sheet metal”—Sides of the sheet metal that when incontact with the other forms a shape.

“the male portion engages the female portion”—When the duct is joinedand formed and the edges are locked into position.

“sealant in the female portion or on the male portion”—Sealant can beadded to the male or female portion.

“creating a seal between the female portion and the maleportion”—Reducing the amount of air leaking from the joint.

“allows the female and male portion to disengage and reengage”—The ductscan be joined and detached as many times as necessary and the sealantretains its ability to reduce or eliminate leakage. The sealant willremain in place as it was originally applied.

“not covered by tape”—The sealant does not require a protective tape inthe end product or during the production process.

“reeves lock”—The locking mechanism as shown in FIG. 1 without thebutton or a notch protruding from the female end. Examples of this canbe seen in SMACNA RL 6A, 6B and 7.

“button lock”—The locking mechanism has a notch (or button) protrudingfrom the female end and is of the type shown in FIG. 1. Examples of thiscan be seen in SMACNA RL 8.

“inserting sealant into the snap lock mechanism”—Applying sealant or agasket to the lock mechanism.

“without the seal failing”—Minimal leakage occurring when subjected topressures not greater than 10 inches of water column or 0.36 psi.Minimal leakage could be less than 10 cfm per linear foot.

“volatile organic compound (VOC)”—Organic chemical compounds that havehigh enough vapor pressures under normal conditions to significantlyvaporize and enter the atmosphere. A wide range of carbon-basedmolecules, such as aldehydes, ketones, and hydrocarbons are VOCs. It ispossible that they can be given off by applying sealant to a duct.

“forming the sheet metal into the shape of a duct”—Giving the sheetmetal the desired shape of the duct.

“the exterior surface does not have sealant”—Absence of any sealantbeing exposed on the outer portion of the duct.

“encapsulated by the sheet metal”—Surrounded by the sheet metalsufficiently that it is not visible from the exterior of the duct ordirectly exposed to the airstream.

“scrap pieces”—Excess pieces of the sealant produced during themanufacturing process.

“reused in the manufacturing process”—Means that pieces can be usedagain in manufacturing such as reliquefying the solidified sealant sothat it can then be placed in the locking mechanism.

“providing sheet metal having a self locking mechanism”—Supplying sheetmetal having a joining mechanism. The sheet metal could be strips or offof a roll.

“sheet metal is provided in strips”—Cut pieces of sheet metal as opposedto coming off of a roll.

“a forming machine”—Machinery capable of forming sheet metal into adesired shape or profile. Examples of this type of machine are machinesmade by Nor, Maplewood, or Lockformer

“machine creates using rolls”—A forming machine that uses rolls tocreate the desired shape or profile.

“folding the sheet metal to create a fold having a gap”—An edge of sheetmetal is formed to create a space.

“each roll forms the sheet metal further lessening the angle of the gapuntil the desired angle”—Each forming roll further forms or changes themetal to create the desired profile.

“forming process”—Making sheet metal into a duct. A nozzle that insertsthe sealant can be used in any part of the forming process.

“in between the 2^(nd) and 8^(th) roll stand”—The nozzle can be placedbetween the 2^(nd) and 8^(th) roll stand in the snap lock formingmachine. The machine could be a Nor type machine.

DESCRIPTION

FIG. 1 shows the profile of a sheet metal duct 2 having a self lockingmechanism 4 which as illustrated in FIG. 1 is a button lock. The selflocking mechanism 4 has a female portion 6 and a male portion 8. Liquidapplied gasketing sealant 10 is in the female portion 6 and is notcovered by tape. FIG. 1 shows the male portion 8 and the female portion6 disengaged. There is a button 12 on female portion 6 making the snaplocking mechanism 4 a button lock. If button 12 was not there, thelocking mechanism would be a reeves lock. It is understood that a personof ordinary skill in the art could alternatively place the sealant onthe male portion 8.

FIG. 2 shows the profile of a sheet metal duct 2 having a snap lockmechanism with the male portion 8 engaged with the female portion 6. Theliquid applied gasketing sealant 10 prevents air from escaping throughthe snap locking mechanism 4. The liquid applied gasketing sealant 10 isencapsulated by the sheet metal duct when the self locking mechanism 4is engaged. The liquid applied gasketing sealant 10 creates a tight fitbetween female portion 6 and male portion 8 which causes a betterconnection for the self locking mechanism 4. The better connection ofthe self locking mechanism 4 reduces vibrations for the duct. Whendifferent temperature air is passed through the duct there is expansionand contraction of the duct. The liquid applied gasketing sealant 10allows for expansion and contraction with minimal vibration because theliquid applied gaskeing sealant 10 pushes the lock into place even withcontraction and expansion. It is important to get the right amount ofliquid applied gasketing sealant 10 on the female portion 6 or the maleportion 8. If too much liquid applied gasketing sealant 10 is appliedthe self locking mechanism 4 may not engage. If too little liquidapplied gasketing sealant 10 is applied, the self locking mechanism 4will not seal properly.

Because the liquid applied gasketing sealant 10 is encapsulated and doesnot leak out of the locking mechanism, the exterior of the duct can bepainted without having to clean or prep or worry about any reactionbetween the liquid applied gasketing sealant 10 and the paint which cancause problems for the paint. Additionally, because the liquid appliedgasketing sealant 10 is not exposed in the interior or exterior of theduct there is no chance that it will attract contaminants that cancontaminate the air stream or the ductwork and/or create potential airquality concerns. The liquid applied gasketing sealant 10 does not comeinto contact with the air stream and does not contaminate it in any way.The liquid applied gasketing sealant 10 does not blow out or leak outwhen under pressure and does not drip out below a temperature of 220° F.and works at temperatures below −80° F. The liquid applied gasketingsealant 10 also has improved aesthetics compared with externally appliedsealant. The liquid applied gasketing sealant 10 is not visible from theoutside of the duct.

Having the liquid applied gasketing sealant 10 on the duct duringmanufacturing lessens the risk of human error of not sealing the metalduct 2 properly or forgetting to seal it. This invention guaranteesenergy efficiency because just by assembling it, the duct is beingsealed. By providing for a self sealing longitudinal seam duringmanufacturing, it prevents the installer from doing additional work inthe air with sealants that off gas (put VOCs into the air). Liquidapplied sealants such as mastics can give off VOCs. The liquid appliedgasketing material 10 does not collect contaminants such as dust andmoisture, which can harbor mold growth. The liquid applied gasketingmaterial 10 does not off gas during operation.

FIG. 3 is a block diagram showing the method of manufacturing sheetmetal. Sheet metal can be on a roll. The sheet metal off of the roll isthen cut to lengths. The cut lengths of sheet metal are then sent to aforming process where an interlocking mechanism is created by rolls (orstands). An injection nozzle is used to insert sealant into or onto thesheet metal. This can be done in any part of the manufacturing process.Preferably it is inserted between the 2^(nd) and 8^(th) roll stand. Itcould be inserted between any of 2^(nd), 3^(rd), 4^(th), 5^(th), 6^(th),7^(th), or 8^(th) stand. Preferably it will be inserted when there is agap angle between 120 and 1 degree. Most preferably it will be insertedin a gap angle between 90 and 10 degrees. Once the sheet metal passesthrough all of the stands and nozzles it then is formed to the desiredshape of the duct.

A typical type of roll stand and how the metal is formed can be seen inFIGS. 4 through 11. It is understood to those skilled in the art thatthe roll forming machine has roll stands on both sides of the machine.The opposite side of the machine not shown in FIG. 4 through 11 formsthe male portion 8 of the self locking mechanism 4. It is understoodthat a person of ordinary skill in the art could take the teachingsshown and apply them so that the liquid applied gasketing material 10could be applied on the male portion of the roll forming press.

Typically snap lock pipe is only endorsed for use in duct systems thatdo not exceed 2″ w.c. of pressure. This is because of the leakage. Thenew sealed pipe is capable of much higher pressures with minimalleakage. It can hold 10 inches water column.

FIG. 12 shows testing results of ducts having the liquid appliedgasketing material vs. ducts without the material. Each test ductconsisted of ten 5′ sections of pipe. The joints were sealed withsealant applied to the inside of the female connection and the outsideof the male connection. The sections were fastened using 3 evenly spacedsheet metal screws. The sealant was given ample time to cure. 6″ and 12″diameter pipe were tested.

The test equipment was a Merriam Instruments digital Smart Manometer anda 3″ calibrated orifice tube. Testing was done at ½″, 1″, 2″, 4″, 6″,and 9″ positive pressures and ½″ and 1″ negative pressure.

Even at lower pressures, there was a significant difference in leakagerates. At 2″ w.c., the unsealed pipe leaked about 25 cfm (0.5 cfm perlinear foot) compared with 1.5 cfm (0.03 cfm per linear foot) for thesealed pipe. This is about a 95% reduction in leakage. FIG. 13 shows achart of the percentage of reduction leakage. FIG. 15 shows data tablesfor the testing.

FIG. 14 shows a nozzle 20. The nozzle 20 has a cylindrical body 22. Thebase 24 has larger diameter than the cylindrical body 22. The upperportion of the cylindrical body 22 has a cut out portion which creates ac-shaped channel 26. The c-shaped channel has notched out sides 28 (onlyone side is shown the other side is matching). There is a passage way 30vertically through the cylindrical body 22 and through a verticalportion 32 of the c-shaped channel 26. The passage extends horizontallythrough a top horizontal section 34 of the c-shaped channel 26. Thenozzle 20 is most preferable place between the 5^(th) and 6^(th) rollstand. This configuration of the nozzle 20 allows it to be placed inbetween the roll stands and be able to inject sealant into the fold ofthe ductwork.

Various changes could be made in the above construction and methodwithout departing from the scope of the invention as defined in theclaims below. It is intended that all matter contained in the abovedescription, as shown in the accompanying drawings, shall be interpretedas illustrative and not as a limitation.

We claim:
 1. A method of manufacturing a sealed circular cross-sectionduct comprising: a) providing an unassembled circular sheet metal ducthaving a self locking longitudinal seam with a reusable liquid appliedsealant positioned within the longitudinal seam while the seam is beingformed; and b) thereafter engaging the longitudinal seam and therebysimultaneously locking the seam to form the circular sheet metal ductand sealing the longitudinal seam without an installer applying sealant.2. A method as recited in claim 1 wherein the sealant has physicalproperties such that it provides a reusable seal so that the selflocking longitudinal seam can be engaged, disengaged and reengaged.
 3. Amethod as recited in claim 1 wherein the self locking longitudinal seamcontains a button lock.
 4. A method as recited in claim 1 wherein theself locking longitudinal seam contains a reeves lock.
 5. A method asrecited in claim 1 wherein the metal duct is capable of a pipe pressureof at least ¼″ water column to 10″ water column without the sealfailing.
 6. A method as recited in claim 1 wherein the sealant does notgive off any volatile organic compound.
 7. A method as recited in claim1 wherein there is no off gassing from the sealant during installationor system operation.
 8. A method as recited in claim 1 wherein anexterior surface of the duct does not have sealant.
 9. A method asrecited in claim 1 wherein the sealant is encapsulated by the sheetmetal so that it is not exposed and does not come into contact with anairstream.
 10. A method as recited in claim 1 wherein the sealant doesnot blow out under pressure or drip out under heat below a temperatureof 220° F.
 11. A method as recited in claim 1 wherein the self lockinglongitudinal seam can be engaged and reengaged and then the exteriorpainted without having to remove excess sealant.
 12. A method as recitedin claim 1 wherein the sealant gives a together fit with the seallocking longitudinal seam so that vibrations are reduced.
 13. A methodas recited in claim 1 wherein the multiple sheet metal ducts areprovided and are stacked in a bundle.
 14. A method as recited in claim 1which permits: a) disengaging the longitudinal seam; b) cutting thecircular sheet metal duct to the appropriates dimension; and c)reengaging the longitudinal seam and simultaneously resealing thelongitudinal seam of the circular duct without an installer usingsealant.
 15. A sealed circular cross-section duct formed by the methodrecited in claim
 1. 16. A sealed circular cross-section duct formed bythe method recited in claim
 2. 17. A sealed circular cross-section ductformed by the method recited in claim
 3. 18. A sealed circularcross-section duct formed by the method recited in claim
 4. 19. A sealedcircular cross-section duct formed by the method recited in claim
 5. 20.A sealed circular cross-section duct formed by the method recited inclaim
 6. 21. A sealed circular cross-section duct formed by the methodrecited in claim
 7. 22. A sealed circular cross-section duct formed bythe method recited in claim
 8. 23. A sealed circular cross-section ductformed by the method recited in claim
 9. 24. A sealed circularcross-section duct formed by the method recited in claim
 10. 25. Asealed circular cross-section duct formed by the method recited in claim11.
 26. A sealed circular cross-section duct formed by the methodrecited in claim
 12. 27. A sealed circular cross-section duct formed bythe method recited in claim
 13. 28. A sealed circular cross-section ductformed by the method recited in claim
 14. 29. A self-sealing circularcross-section sheet metal duct comprising: a) an unassembled circularsheet metal duct having a self locking longitudinal seam with a reusableliquid applied sealant positioned within the longitudinal seam while theseam is being formed; and b) thereafter causing the longitudinal seam tobe engaged and thereby simultaneously locking the seam to form thecircular sheet metal duct and sealing the longitudinal seam without aninstaller applying a sealant.
 30. A self-sealing circular cross-sectionsheet metal duct as recited in claim 29 wherein the sealant has physicalproperties such that it provides a reusable seal so that the selflocking longitudinal seam can be engaged, disengaged and reengaged. 31.A self-sealing circular cross-section sheet metal duct as recited inclaim 29 wherein the self locking longitudinal seam contains a buttonlock.
 32. A self-sealing circular cross-section sheet metal duct asrecited in claim 29 wherein the self locking longitudinal seam containsa reeves lock.
 33. A self-sealing circular cross-section sheet metalduct as recited in claim 29 wherein the metal duct is capable of a pipepressure of at least ¼″ water column to 10″ water column without theseal failing.
 34. A self-sealing circular cross-section sheet metal ductas recited in claim 29 wherein the sealant does not give off anyvolatile organic compound.
 35. A self-sealing circular cross-sectionsheet metal duct as recited in claim 29 wherein there is no off gassingfrom the sealant during installation or system operation.
 36. Aself-sealing circular cross-section sheet metal duct as recited in claim29 wherein an exterior surface of the duct does not have sealant.
 37. Aself-sealing circular cross-section sheet metal duct as recited in claim29 wherein the sealant is encapsulated by the sheet metal so that it isnot exposed and does not come into contact with an airstream.
 38. Aself-sealing circular cross-section sheet metal duct as recited in claim29 wherein the sealant does not blow out under pressure or drip outunder heat below a temperature of 220° F.
 39. A self-sealing circularcross-section sheet metal duct as recited in claim 29 wherein the selflocking longitudinal seam can be engaged and reengaged and then theexterior painted without having to remove excess sealant.
 40. Aself-sealing circular cross-section sheet metal duct as recited in claim29 wherein the sealant gives a tighter fit with the self lockinglongitudinal seam so that vibrations are reduced.
 41. A self-sealingcircular cross-section sheet metal duct as recited in claim 29 whereinunassembled multiple sheet metal ducts are provided and are stacked in abundle.
 42. A self-sealing circular cross-section sheet metal duct asrecited in claim 29 which permits: a) disengaging the longitudinal seam;b) cutting the circular sheet metal duct to the appropriate dimension;and c) reengaging the longitudinal seam and simultaneously resealing thelongitudinal seam of the circular duct without an installer applyingsealant.